The known photopolymerizable systems contain a photoinitiator possessing in the molecule a functional group that, by electromagnetic excitation, generally UV radiation, produces radicals able to polymerize the system.
In EP 3002 A numerous alpha-hydroxyketons are described together with their uses as photoinitiators; particularly in Example 5 the use as photoinitiator of 2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl) phenoxy]-phenyl}-2-methyl-propan-1-one (compound No. 21), obtained in form of wax and with boiling point of 220° C. at 0.05 mmHg, is described.